1. Field of the Invention
The present invention relates to contact lenses, and more particularly pertains to soft contact lens of the toric type that incorporates meniscus-shaped top and bottom flattened zones to dynamically stabilize the orientation of the lens.
2. Description of the Related Art
It is understood that the correction of certain optical defects can be achieved through presenting non-spherical corrective characteristics into a contact lens, such as cylindrical, bifocal, or multifocal, which may be problematic in that the contact lens need to be maintained at a specific orientation while on the eye to be effective. Nonetheless, because of the effects of blinking, eyelids, and tear fluid movement, the lens will rotate on the eye.
Lenses designed to maintain an on-eye orientation are typically categorized into two types. One type uses static stabilization to maintain lens orientation. Examples of the static stabilization methods include prismatic balancing, thickening the lower lens edge, supporting the lens on the lower eyelid, forming depressions or elevations on the lens' surface, and tapering off the lens edge.
A second type uses the movement of the eyelids to dynamically stabilize in maintaining lens orientation. Methods of the dynamic stabilization include reducing the thickness of outer surface of the lens at two symmetrical regions, thickening the two outer regions in the horizontal center axis, and flattening top and bottom regions of the lens.
The known methods for maintaining lens orientation suffer from several defects, wherein a disadvantage is demanding specialized tools for production; moreover, lenses by these methods are uncomfortable to wear, for example, in the tapered-off method that causes a sharp edge of the lens, which would distress the wearers. Therefore, in the Taiwanese Patent Publication No. 424168 by Timothy A. Clutterbuck, a dynamically stabilized contact lens is disclosed, wherein the lens incorporates variably-shaped lenticular zones, freeing the production from specialized tools and comforting the wearers while wearing.
However, the dynamically stabilized contact lenses mentioned above exhibit that the difference in thickness between the flattened and un-flattened zones on left and right sides of the lens is not apparent, and, that is to say, the flattened regions are considerably wider than the un-flattened regions on both sides, so that the little variance in thickness causes the lens rotating when the eyelids are blinking. Hence, the toric contact lens is weak in stabilizing its lens orientation. The required tools for the production of the lens include convex inserter and convex inserter carrier (the so-called rear mold section by one skilled in the art). Since the lenticular regions of the convex inserter is tough to form positional marks, it is then laborious to align the inserter with the inserter carrier, and, subsequently, giving rise to the deviation of astigmatic angle while in the production; moreover, without marking a wearing sign on the lens, it is troublesome for the wearers with astigmatism.
It is accordingly the object of the present invention to provide a toric contact lens with meniscus-shaped top and bottom flattened zones to dynamically stabilize the orientation of the lens, which will considerably augment the stability of angular orientation of the lens, ease the alignment for the positional lines of the inserter and the carrier, and offer the wearers handy way to carry on the toric contact lenses.